Hybrids such as Toyota’s Prius have become a common sight. Now major automakers are proposing a next generation of hybrids that can be plugged in to extend their electric range and vastly improve fuel economy. This interactive graphic shows how conventional hybrids work, as well as how two versions of these proposed plug-in hybrids, one labeled “Plug-in Hybrid” and the other “Extended-Range Electric,” work. Each of these plug-in hybrids operates differently when the battery is charged versus when it is largely depleted. Click on one of the five buttons above to view animations of how the vehicles operate under different driving conditions. Each vehicle operates during a stylized drive cycle, starting at low speeds, accelerating to highway speeds, and then decelerating to a stop. If at any time you’d like to pause the animation or select a different part of the drive cycle, click on the appropriate section of the graph at the bottom right of the graphic.

The first type of plug-in hybrid, labeled “Plug-in Hybrid,” is basically a conventional hybrid vehicle with a larger battery pack. Companies such as Toyota and Ford are developing hybrids of this type. For heavy acceleration and high speed, these vehicles rely on power from both an internal combustion engine and an electric motor. But a larger battery pack in plug-in hybrids allows them to rely much more on electricity than conventional hybrids do.

“Extended-Range Electric” vehicles represent a radical departure from conventional hybrids. Whereas in conventional hybrids, the wheels are turned by an electric motor, a gasoline engine, or both, the wheels in these new cars will be turned only by a large electric motor. For short trips, the motor will run on battery power alone. For longer trips, a gasoline-powered generator kicks in to supply electricity.